Cu-base amorphous alloy

ABSTRACT

The present invention provides Cu-base amorphous alloys comprising an amorphous phase of 90% or more by volume fraction. The amorphous phase has a composition represented by the formula: Cu 100−a−b (Zr+Hf) a Ti b  or Cu 100−a−b−c−d (Zr+Hf) a Ti b M c T d , wherein M is one or more elements selected from the group consisting of Fe, Cr, Mn, Ni, Co, Nb, Mo, W, Sn, Al, Ta and rare earth elements, T is one or more elements selected from the group consisting of Ag, Pd, Pt and Au, and a, b, c and d are atomic percentages falling within the following ranges: 5&lt;a≦55, 0≦b≦45, 30&lt;a+b≦60, 0.5≦c≦5, 0≦d≦10. The Cu-base amorphous alloy has a high glass-forming ability as well as excellent mechanical properties and formability, and can be formed as a rod or plate material with a diameter or thickness of 1 mm or more and an amorphous phase of 90% or more by volume fraction, through a metal mold casting process.

TECHNICAL FIELD

[0001] The present invention relates to a Cu-base amorphous alloy having a high glass-forming ability as well as excellent mechanical properties and formability.

BACKGROUND ART

[0002] It is well known that an alloy in its molten state can be rapidly cooled or quenched to obtain an amorphous solid in various forms, such as thin strip, filament or powder/particle. An amorphous alloy thin-strip or powder can be prepared through various processes, such as a single-roll process, a twin-roll process, an in-rotating liquid spinning process and an atomization process, which can provide a high quenching rate. Heretofore, a number of Fe, Ti, Co, Zr, Ni, Pd or Cu-base amorphous alloys have been developed, and their specific properties such as excellent mechanical properties and high corrosion resistance have been clarified.

[0003] In regard to Cu-base amorphous alloys related to the present invention, researches have been mainly made on binary alloys such as Cu-Ti and Cu-Zr, or ternary alloys such as Cu-Ni-Zr, Cu-Ag-RE, Cu-Ni-P, Cu-Ag-P, Cu-Mg-RE and Cu-(Zr, RE, Ti)-(Al, Mg, Ni) (Japanese Patent Laid-Open Publication Nos. H07-41918, H07-173556, H09-59750 and H11-61289; Sic. Rep. RITU. A42 (1996) 1343-1349; Sic. Rep. RITU. A28 (1980) 225-230; Mater. Sic. Eng. A181-182 (1994) 1383-1392; Mater. Trans. JIM, 37 (1996) 359-362).

[0004] While the above Cu-base amorphous alloys have been researched based largely on thin-strip samples prepared through the aforementioned single-roll/liquid quenching process, research and development on Cu-base bulk amorphous alloys for practical use, or Cu-base bulk amorphous alloys excellent in glass-forming ability, has made few advance.

DISCLOSURE OF THE INVENTION

[0005] It is known that an amorphous alloy undergoing a glass transition with a wide supercooled liquid region and having a high reduced-glass-transition temperature (Tg/Tm) exhibits an excellent stability against crystallization and a high glass-forming ability. The alloy having such a high glass-forming ability can be formed as a bulk amorphous alloy through a metal mold casting process. It is also known that when a specific amorphous alloy is heated, the viscosity of the amorphous alloy is sharply lowered during transition to the supercooled liquid state before crystallization.

[0006] Such an amorphous alloy can be formed in an arbitrary shape through a closed forging process or the like by taking advantage of the lowered viscosity in the supercooled liquid state. Thus, it can be said that an alloy having a wide supercooled liquid region and a high reduced-glass-transition temperature (Tg/Tm) exhibits a high glass-forming ability and an excellent formability.

[0007] The conventional Cu-base amorphous alloys have a poor glass-forming ability, and have been able to be formed only in limited forms, such as thin strip, powder and thin line, through a liquid quenching process. In addition, they have no stability at high temperature, and have difficulty in being converted into a final product with a desired shape, resulting in their quite limited industrial applications.

[0008] In view of the above circumstance, it is an object of the present invention to provide a Cu-base amorphous alloy having a high glass-forming ability as well as excellent mechanical properties and formability.

[0009] Through various researches on the optimal composition of Cu-base alloy for achieving the above object, the inventors found that a Cu-base alloy having a specific composition containing Zr and/or Hf can be molten and then rapidly solidified from the liquid state to obtain a Cu-base amorphous alloy having a high glass-forming ability as well as excellent mechanical properties and formability, such as a rod-shaped (or plate-shaped) amorphous- phase material with 1 mm or more of diameter (or thickness). Based on this knowledge, the inventors have completed the present invention.

[0010] Specifically, according to a first aspect of the present invention, there is provided a Cu-base amorphous alloy comprising an amorphous phase of 90% or more by volume fraction. The amorphous phase has a composition represented by the following formula:

Cu^(100−a−b)(Zr+Hf)_(a)Ti_(b)

[0011] , wherein a and b are atomic percentages falling within the following ranges: 5<a≦55, 0≦b≦45, 30<a+b≦60 . In this formula, (Zr+Hf) means Zr and/or Hf.

[0012] According to a second aspect of the present invention, there is provided a Cu-base amorphous alloy comprising an amorphous phase of 90% or more by volume fraction. The amorphous phase has a composition represented by the following formula:

Cu_(100−a−b)(Zr+Hf)_(a)Ti_(b)

[0013] wherein a and b are atomic percentages falling within the following ranges: 10<a≦40, 5≦b≦30, 35≦a+b≦50.

[0014] According to a third aspect of the present invention, there is provided a Cu-base amorphous alloy comprising an amorphous phase of 90% or more by volume fraction. The amorphous phase has a composition represented by the following formula:

Cu_(100−a−b−c−d)(Zr+Hf)_(a)Ti_(b)M_(c)T_(d)

[0015] , wherein M is one or more elements selected from the group consisting of Fe, Cr, Mn, Ni, Co, Nb, Mo, W, Sn, Al, Ta and rare earth elements, T is one or more elements selected from the group consisting of Ag, Pd, Pt and Au, and a, b, c and d are atomic percentages falling within the following ranges: 5<a≦55, 0≦b≦45, 30<a+b≦60, 0.5≦c≦5, 0≦d≦10.

[0016] According to a fourth aspect of the present invention, there is provided a Cu-base amorphous alloy comprising an amorphous phase of 90% or more by volume fraction. The amorphous phase has a composition represented by the following formula:

Cu_(100−a−b−c−d)(Zr+Hf)_(a)Ti_(b)M_(c)T_(d)

[0017] , wherein M is one or more elements selected from the group consisting of Fe, Cr, Mn, Ni, Co, Nb, Mo, W, Sn, Al, Ta and rare earth elements, T is one or more elements selected from the group consisting of Ag, Pd, Pt and Au, and a, b, c and d are atomic percentages falling within the following ranges: 10<a≦40, 5≦b≦30, 35≦a+b≦50, 0.5≦c≦5, 0≦d≦10.

[0018] The above Cu-base amorphous alloys of the present invention may have a supercooled liquid region with a temperature interval ΔTx of 25 K or more. The temperature interval is represented by the following formula: ΔTx=Tx−Tg, wherein Tx is a crystallization temperature of the alloy, and Tg is a glass transition temperature of the alloy.

[0019] The Cu-base amorphous alloys of the present invention may have a reduced glass transition temperature of 0.56 or more. The reduced glass transition temperature is represented by the following formula: Tg/Tm, wherein Tg is a glass transition temperature of the alloy, and Tm is a melting temperature of the alloy.

[0020] The Cu-base amorphous alloys of the present invention may be formed as a rod or plate material having a diameter or thickness of 1 mm or more and an amorphous phase of 90% or more by volume fraction, through a metal mold casting process.

[0021] The Cu-base amorphous alloys of the present invention may have a compressive fracture strength of 1800 MPa or more, an elongation of 1.5% or more, and a Young's modulus of 100 GPa or more.

[0022] The term “supercooled liquid region” herein is defined by the difference between a glass transition temperature of the alloy and a crystallization temperature (or an initiation temperature of crystallization) of the alloy, which are obtained from a differential scanning calorimetric analysis performed at a heating rate of 40 K/minute. The “supercooled liquid temperature region” is a numerical value indicative of resistibility against crystallization which is equivalent to thermal stability of amorphous state, glass-forming ability or formability. The alloys of the present invention have a supercooled liquid temperature region ΔTx of 25 K or more.

[0023] The term “reduced glass transition temperature” herein is defined by a ratio of the glass transition temperature (Tg) to a melting temperature (Tm) of the alloy which is obtained from a differential scanning calorimetric analysis (DTA) performed at a heating rate of 5 K/minute. The “reduced glass transition temperature” is a numerical value indicative of the glass-forming ability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a graph showing a composition range of Cu-Zr-Ti ternary alloys capable of forming a bulk amorphous material and the critical thickness (unit: mm) of the bulk amorphous materials.

[0025]FIG. 2 is a graph showing a stress-strain curve in a compression test of a Cu₆₀Zr₂₀Ti₂₀ bulk amorphous alloy having a diameter of 2 mm.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] One embodiment of the present invention will now be described.

[0027] In a Cu-base amorphous alloy of the present invention, Zr and/or Hf are basic elements for forming an amorphous material. The content of Zr and/or Hf is set in the range of greater than 5 atomic % up to 55 atomic %, preferably in the range of 10 to 40 atomic %. If the content of Zr and/or Hf is reduced to 5 atomic % or less or increased to greater than 55 atomic %, the supercooled liquid region ΔTx and the reduced glass transition temperature Tg/Tm will be reduced, resulting in deteriorated glass-forming ability.

[0028] Element Ti is effective to enhance the glass-forming ability to a large degree. However, if the content of Ti is increased to greater than 45 atomic %, the supercooled liquid region ΔTx and the reduced glass transition temperature Tg/Tm will be reduced, resulting in deteriorated glass-forming ability. Thus, the content of Ti is set in the range of 0 to 45 atomic %, preferably 5 to 30 atomic %.

[0029] The total of the content of Zr and/or Hf and the content of Ti is set in the range of greater than 30 atomic % up to 60 atomic %. If the total content of these elements is reduced to 30 atomic % or increased to greater than 60 atomic %, the glass-forming ability will be deteriorated, and no bulk material can be obtained. Preferably, the total content is set in the range of 35 to 50 atomic %.

[0030] Cu of up to 10 atomic % may be substituted with one or more element selected from the group consisting of Ag, Pd, Au and Pt. This substitution can slightly increase the temperature interval of the supercooled liquid region. If greater than 10 atomic % of Cu is substituted, the supercooled liquid region will be reduced to less than 25 K, resulting in deteriorated glass-forming ability.

[0031] While a small amount of one or more elements selected from the group consisting of Fe, Cr, Mn, Ni, Co, Nb, Mo, W, Sn, Al, Ta and rare earth elements (Y, Gd, Tb, Dy, Sc, La, Ce, Pr, Nd, Sm, Eu and Ho) may be effectively added to provide an enhanced mechanical strength, the glass-forming ability is deteriorated as the addition of these elements is increased. Thus, the content of these element is preferably set in the range of 0.5 to 5 atomic %.

[0032]FIG. 1 shows a composition range of Cu-Zr-Ti ternary alloys capable of forming a bulk amorphous material and the critical thickness of the bulk amorphous materials. The composition range capable of forming a bulk amorphous material (having a diameter of 1 mm or more) is shown by the solid line. The numeral in the circle indicates the maximum thickness (unit:mm) of the bulk amorphous materials to be formed in the bulk amorphous materials. FIG. 2 shows a stress-strain curve in a compression test of a Cu₆₀Zr₂₀Ti₂₀ bulk amorphous alloy. This alloy has a compressive fracture strength of about 2000 MPa, an elongation of 2.5%, and a Young's modulus of 122 GPa.

[0033] The Cu-base amorphous alloy of the present invention can be cooled and solidified from its molten state through various processes, such as a single-roll process, a twin-roll process, an in-rotating liquid spinning process and an atomization process, to provide an amorphous solid in various forms, such as thin strip, filament or powder/particle. The Cu-base amorphous alloys of the present invention can also be formed as a bulk amorphous alloy having an arbitrary shape through not only the above conventional processes but also a process of filling a molten metal in a metal mold and casting therein by taking advantage of its high glass-forming ability.

[0034] For example, in a typical metal mold casting process, a mother alloy prepared to have the alloy composition of the present invention is molten in a silica tube under argon atmosphere. Then, the molten alloy is filled in a copper mold at an injection pressure of 0.5 to 1.5 kg · f/cm², and solidified so as to obtain an amorphous alloy ingot. Alternatively, any other suitable method such as a die-casting process or a squeeze-casting process may be used.

EXAMPLE

[0035] Examples of the present invention will be described below. For each of materials having alloy compositions as shown in Table 1 (Inventive Examples 1 to 17 and Comparative Examples 1 to 4), a corresponding mother alloy was molten through an arc-melting process, and then a thin-strip sample of about 20 μm thickness was prepared through a single-roll/liquid quenching process. Then, the glass transition temperature (Tg) and the crystallization temperature (Tx) of the thin-strip sample were measured by a differential scanning calorimeter (DSC). Based on these measured values, the supercooled liquid region ΔTx (=Tx−Tg) of the thin-strip sample was calculated. The melting temperature (Tm) of the sample was also measured by a differential scanning calorimetric analysis (DTA). Then, the reduced glass transition temperature (Tg/Tm) of the sample was calculated from the obtained glass transition temperature and the melting temperature.

[0036] Further, a rod-shaped sample of 1 mm diameter was prepared for each of the above materials, and the amorphous phase in the rod-shaped sample was determined through an X-ray diffraction method. The volume fraction (Vf-amo.) of the amorphous phase in the sample was also evaluated by comparing the calorific value of the sample during crystallization with that of a completely vitrified thin strip of about 20 μm thickness, by use of DSC. These evaluation results are shown in Table 1. Further, a compression test piece was prepared for each of the above materials, and the test piece was subjected to a compression test using an Instron-type testing machine to evaluate the compressive fracture strength (σ f), the Young's modulus (E) and the elongation (ε) of the test piece. The Vickers hardness (Hv) was also measured. These evaluation results are shown in Table 2. TABLE 1 Alloy Composition Tg Tx Tx − Tg Vf-Amo. (at %) (K) (K) (K) Tg/Tm (%) Inventive Example 1 Cu₆₅Zr₂₅Ti₁₀ 726 765 39 0.58 100 Inventive Example 2 Cu₆₀Zr₄₀ 722 777 55 0.60  91 Inventive Example 3 Cu₆₀Zr₃₀Ti₁₀ 713 750 37 0.62 100 Inventive Example 4 Cu₆₀Zr₂₀Ti₂₀ 708 743 35 0.63 100 Inventive Example 5 Cu₆₀Zr₁₀Ti₃₀ 688 719 31 0.58 100 Inventive Example 6 Cu₅₅Zr₃₅Ti₁₀ 680 727 47 0.59 100 Inventive Example 7 Cu₆₅Hf₂₅Ti₁₀ 760 797 37 0.57 100 Inventive Example 8 Cu₆₀Hf₃₀Ti₁₀ 747 814 67 0.61 100 Inventive Example 9 Cu₆₀Hf₂₀Ti₂₀ 730 768 38 0.62 100 Inventive Example 10 Cu₆₀Hf₁₀Ti₃₀ 696 731 35 0.59 100 Inventive Example 11 Cu₅₅Hf₃₀Ti₁₅ 727 785 58 0.59 100 Inventive Example 12 Cu₆₀Zr₁₅Hf₁₅Ti₁₀ 729 784 55 0.61 100 Inventive Example 13 Cu₆₀Zr₁₀Hf₁₀Ti₂₀ 716 753 37 0.63 100 Inventive Example 14 Cu₆₀Zr₂₈Ti₁₀Nb₂ 724 757 33 0.59  95 Inventive Example 15 Cu₆₀Zr₂₇Ti₁₀Sn₃ 837 877 40 0.61  95 Inventive Example 16 Cu₆₀Zr₂₇Ti₁₀Ni₃ 719 754 35 0.60  94 Inventive Example 17 Cu₆₀Zr₂₅Ti₁₀Ni₅ 708 749 41 0.60 100 Comparative Example 1 Cu₇₀Zr₂₀Ti₁₀ 746    50< Comparative Example 2 Cu₇₀Hf₂₀Ti₁₀ 771    50< Comparative Example 3 Cu₆₀Zr₂₀Ti₁₀Ni₁₀ 762    50< Comparative Example 4 Cu₆₀Ti₄₀ 694    50<

[0037] As seen in Table 1, each of the amorphous alloys of Inventive Examples exhibited a supercooled liquid region ΔTx (=Tx−Tg) of 25 K or more and a reduced glass transition temperature (Tg/Tm) of 0.56 or more, and could be readily formed as an amorphous alloy rod of 1 mm diameter.

[0038] In contrast, each of the amorphous alloys of Comparative Examples 1 and 2, in which the total of the content of Zr and/or Hf and the content of Ti is 30 atomic %, exhibited no glass transition, and no amorphous alloy rod of 1 mm diameter could be formed therefrom due to its poor glass-forming ability. The amorphous alloy of Comparative Example 3, in which the content of Ni is 10 atomic %, exhibited no glass transition, and no amorphous alloy rod of 1 mm diameter could be formed therefrom due to its poor glass-forming ability. While the amorphous alloy of Comparative Example 4 containing no basic element Zr and/or Hf was vitrified in the form of a ribbon prepared through a single-roll process at a high cooling rate, no amorphous alloy rod of 1 mm diameter could be formed therefrom, and the compression test could not be conducted. TABLE 2 Alloy Composition σ f E ε (at %) (MPa) (GPa) (%) Hv Inventive Example 1 Cu₆₅Zr₂₅Ti₁₀ 1970 108 2.0 603 Inventive Example 2 Cu₆₀Zr₄₀ 1880 102 2.7 555 Inventive Example 3 Cu₆₀Zr₃₀Ti₁₀ 2115 124 3.2 504 Inventive Example 4 Cu₆₀Zr₂₀Ti₂₀ 2015 140 2.6 556 Inventive Example 5 Cu₆₀Zr₁₀Ti₃₀ 2010 135 1.7 576 Inventive Example 6 Cu₅₅Zr₃₅Ti₁₀ 1860 112 2.8 567 Inventive Example 7 Cu₆₅Hf₂₅Ti₁₀ 2145 142 1.8 698 Inventive Example 8 Cu₆₀Hf₃₀Ti₁₀ 2143 134 1.9 592 Inventive Example 9 Cu₆₀Hf₂₀Ti₂₀ 2078 135 2.1 620 Inventive Example Cu₆₀Hf₁₀Ti₃₀ 2260 126 1.8 650 10 Inventive Example Cu₅₅Hf₃₀Ti₁₅ 2175 114 2.0 681 11 Inventive Example Cu₆₀Zr₁₅Hf₁₅Ti₁₀ 2100 121 2.4 640 12 Inventive Example Cu₆₀Zr₁₀Hf₁₀Ti₂₀ 2110 136 2.2 647 13 Inventive Example Cu₆₀Zr₂₈Ti₁₀Nb₂ 2204 129 2.0 574 14 Inventive Example Cu₆₀Zr₂₇Ti₁₀Sn₃ 2145 125 1.8 519 15 Inventive Example Cu₆₀Zr₂₇Ti₁₀Ni₃ 2130 128 2.1 556 16 Inventive Example Cu₆₀Zr₂₅Ti₁₀Ni₅ 1915 113 2.4 531 17 Comparative Cu₇₀Zr₂₀Ti₁₀ 564 Example 1 Comparative Cu₇₀Hf₂₀Ti₁₀ 624 Example 2 Comparative Cu₆₀Zr₂₀Ti₁₀Ni₁₀ 578 Example 3 Comparative Cu₆₀Ti₄₀ 566 Example 4

[0039] As seen in Table 2, each of the amorphous alloys of Inventive Examples exhibited a compressive fracture strength (σ f) of 1800 MPa or more, an elongation (ε) of 1.5% or more, and a Young's modulus (E) of 100 GPa or more.

[0040] Further, for each of materials having alloy compositions as shown in Table 3 (Inventive Examples 18 to 32 and Comparative Examples 5 to 8), a corresponding mother alloy was molten through an arc-melting process, and then a rod-shaped sample with an amorphous single phase was prepared through a metal mold casting process. Then, the critical thickness and the critical diameter of the rod-shaped sample were measured. A compression test piece was also prepared for each of the above materials, and the test piece was subjected to a compression test using an Instron-type testing machine to evaluate the compressive fracture strength (σ f). These results are shown in Table 3. TABLE 3 Compressive Fracture Critical Thickness Alloy Composition Strength (σ f) Critical Diameter* (at %) (MPa) (mm) Inventive Example 18 Cu₅₈Zr₂₀Hf₁₀Ti₁₀Gd₂ 2000 3 Inventive Example 19 Cu₅₈Zr₂₀Hf₁₀Ti₁₀Al₂ 2200 3 Inventive Example 20 Cu₅₈Zr₂₀Hf₁₀Ti₁₀Sn₂ 2200 4 Inventive Example 21 Cu₅₈Zr₂₀Hf₁₀Ti₁₀Ta₂ 2250 4 Inventive Example 22 Cu₅₈Zr₂₀Hf₁₀Ti₁₀W₂ 2300 3 Inventive Example 23 Cu₆₀Zr₂₉Ti₉Gd₂ 2150 4 Inventive Example 24 Cu₆₀Hf₂₄Ti₁₄Y₂ 2400 5 Inventive Example 25 Cu₆₀Hf₂₄Ti₁₄Gd₂ 2430 3 Inventive Example 26 Cu₅₈Zr₂₉Ti₉Fe₂Y₂ 2000 3 Inventive Example 27 Cu₅₈Zr₂₉Ti₉Cr₂Gd₂ 2300 3 Inventive Example 28 Cu₅₈Hf₂₄Ti₁₄Mn₂Y₂ 2100 2 Inventive Example 29 Cu₅₈Zr₂₈Ti₉Fe₂Y₂Ag₁ 2100 3 Inventive Example 30 Cu₅₈Zr₂₈Ti₉Cr₂Gd₂Au₁ 2100 3 Inventive Example 31 Cu₅₈Hf₂₂Ti₁₄Mn₂Y₂Pd₂ 2210 4 Inventive Example 32 Cu₅₈Zr₁₈Hf₁₀Ti₁₀Gd₂Pt₂ 2300 5 Comparative Example 5 Cu₇₀Zr₂₀Ti₁₀ *0.100 Comparative Example 6 Cu₇₀Hf₂₀Ti₁₀ *0.100 Comparative Example 7 Cu₇₅Zr₁₅Ti₁₀ *0.050 Comparative Example 8 Cu₇₅Hf₁₅Ti₁₀ *0.050

[0041] As seen in Table 3, the critical thickness in Comparative Examples is 0.1 mm at the highest, whereas Inventive Examples have a critical thickness of 2 mm or more, and a compressive fracture strength of 2000 MPa or more. This result verifies that Inventive Examples added with rare earth elements represented by M in the aforementioned formula can be formed as an amorphous alloy excellent in glass-forming ability and mechanical properties.

Industrial Applicability

[0042] As mentioned above, according to the Cu-base amorphous alloy composition of the present invention, a rod-shaped sample having a diameter (thickness) of 1 mm or more can be readily prepared through a metal mold casting process. The amorphous alloy exhibits a supercooled liquid region of 25 K or more, and has high strength and Young's modulus. Thus, the present invention can provide a practically useful Cu-base amorphous alloy having a high glass-forming ability as well as excellent mechanical properties and formability. 

What is claimed is:
 1. A Cu-base amorphous alloy comprising an amorphous phase of 90% or more by volume fraction, said amorphous phase having a composition represented by the following formula: Cu_(100−a−b)(Zr+Hf)_(a)Ti_(b) , wherein a and b are atomic percentages falling within the following ranges: 5<a≦55 0≦b≦45 30<a+b≦60
 2. A Cu-base amorphous alloy comprising an amorphous phase of 90% or more by volume fraction, said amorphous phase having a composition represented by the following formula: Cu_(100−a−b)(Zr+Hf)_(a)Ti_(b) , wherein a and b are atomic percentages falling within the following ranges: 10<a≦40 5≦b≦30 35≦a+b≦50
 3. A Cu-base amorphous alloy comprising an amorphous phase of 90% or more by volume fraction, said amorphous phase having a composition represented by the following formula: Cu_(100−a−b−c−d)(Zr+Hf)_(a)Ti_(b)M_(c)T_(d) , wherein M is one or more elements selected from the group consisting of Fe, Cr, Mn, Ni, Co, Nb, Mo, W, Sn, Al, Ta and rare earth elements, T is one or more elements selected from the group consisting of Ag, Pd, Pt and Au, and a, b, c and d are atomic percentages falling within the following ranges: 5<a≦55 0≦b≦45 30<a+b≦60 0.5≦c≦5 0≦d≦10
 4. A Cu-base amorphous alloy comprising an amorphous phase of 90% or more by volume fraction, said amorphous phase having a composition represented by the following formula: Cu_(100−a−b−c−d)(Zr+Hf)_(a)Ti_(b)M_(c)T_(d) , wherein M is one or more elements selected from the group consisting of Fe, Cr, Mn, Ni, Co, Nb, Mo, W, Sn, Al, Ta and rare earth elements, T is one or more elements selected from the group consisting of Ag, Pd, Pt and Au, and a, b, c and d are atomic percentages falling within the following ranges: 10<a≦40 5≦b≦30 35≦a+b≦50 0.5≦c≦5 0≦d≦10
 5. The Cu-base amorphous alloy as defined in either one of claims 1 to 4, which has a supercooled liquid region with a temperature interval ΔTx of 25 K or more, said temperature interval being represented by the following formula: ΔTx=Tx−Tg , wherein Tx is a crystallization temperature of said alloy, and Tg is a glass transition temperature of said alloy.
 6. The Cu-base amorphous alloy as defined in either one of claims 1 to 5, which has a reduced glass transition temperature of 0.56 or more, said reduced-glass-transition temperature being represented by the following formula: Tg/Tm , wherein Tg is a glass transition temperature of said alloy, and Tm is a melting temperature of said alloy.
 7. The Cu-base amorphous alloy as defined in either one of claims 1 to 6, which is formed as a rod or plate material having a diameter or thickness of 1 mm or more and an amorphous phase of 90% or more by volume fraction, through a metal mold casting process.
 8. The Cu-base amorphous alloy as defined in either one of claims 1 to 7, which has a compressive fracture strength of 1800 MPa or more, an elongation of 1.5% or more, and a Young's modulus of 100 GPa or more. 